1. Field of the Invention
The invention is directed to machinery for overlapping or shingling cut sheets as they are fed to a stacking station and, more particularly, relates to a slowdown mechanism in the overlapping process to eliminate sheet lead edge contact and consequent damage in the overlapping zone and the stacking station.
2. The Prior Art
In the paper-cutting machinery field, it is common for cut sheets to be shingled enroute to a stacking or collection station. The overlapping or shingling operation is usually performed by high and low-speed tape systems. The speed of the leading sheet is reduced as it is fed onto the low-speed tape by some suitable means, such as a stop roll. One example of this stop roll shingling process is illustrated in U.S. Pat. No. 3,554,534, where a snap down roll is also disposed upstream of the stop roll to deflect the tail ends of sheets passing onto the low-speed tape down and out of the way of the next oncoming sheet being delivered by the high-speed tape system.
A serious drawback with presently known sheet overlap systems is that, as sheet delivery speed goes up, it becomes impossible to overlap sheets enough to eliminate lead edge damage. At high sheeter speeds, approximately 400-1500 fpm, lead edge damage occurs not only in the collection or stacking station but also at the stop rolls in the overlap area. In the case of the stop rolls, sheets being delivered at high speed tend to impact against the low-speed stop roll which can cause wrinkling in the sheets and may even lead to jam-ups in the sheet delivery system.
The present invention is directed to apparatus for effectively eliminating the problem of lead edge damage even at high sheet speeds, either in the overlap area and/or the collection station.